A rotating electric machine in which a cooler for cooling a coolant is provided has been described, for example, in Japanese Patent Laid-open Nos. Hei 7-177705 and Hei 10-146022. The rotating electric machine described in these documents is configured such that a space between a stator frame and a stator iron core is partitioned into a low temperature gas chamber, to which a coolant at a low temperature is supplied, and a high temperature gas chamber, in which the heated coolant flows. A plurality of coolers distributed in the axial direction are provided in a foundation pit under the rotating electric machine, whereby the coolant cooled by the plurality of coolers and boosted by a ventilating fan is introduced to various heat sources, such as the iron core and the coils, via the low temperature gas chamber, and the coolant which has been used for cooling the heat sources is returned to the coolers via the high temperature gas chamber.
The above-described rotating electric machine, however, has a problem. Since the coolant which has passed through one or two or more of the heat sources is then introduced to a central portion of the iron core, the temperature of the coolant is raised before the coolant reaches the central portion of the iron core. Accordingly, for the above-described rotating electric machine, if a thermal load generated from the heat sources, such as the iron core and coils, becomes large with an increase in the generation capacity or in the loss density, the cooling effect of the coolant introduced to the central portion of the iron core is significantly degraded. As a result, in the above-described rotating electric machine, there is a possibility that local heat generation will occur in a gap between the stator iron core and a rotor iron core, thereby to increase the thermal oscillation stroke of the rotor due to uneven thermal expansion of the rotor in the axial direction.
To solve the above-described problem, there may be considered a method of increasing the amount of the coolant or optimizing the distribution of the amounts of the coolant components supplied to respective ventilating passages by adjusting the ventilating resistance; however, according to the former method, the ventilation loss of the coolant caused upon boosting the coolant by the fan becomes larger, to increase the total loss in the coolant; and, according to the latter method, since the ventilation resistance must be adjusted while the desired electric and mechanical characteristics are satisfied in a limited space, it is difficult to optimize the distribution of the coolant components supplied to the respective ventilating passages.